This invention is directed to a crossed-field switch device, and particularly a crossed-field switch device which has a localized auxiliary magnetic field which can be turned on for off-switching.
A considerable amount of experimentation and development has been done by the research and development group with which the present inventor has been associated. The crossed-field switch device has been developed from a laboratory curiosity into an off-switching device which is capable of off-switching high current against high voltage. Prototype tubes have been developed which are capable of off-switching 10,000 amperes against 100 kilovolts without requiring a natural current zero for arc quenching. In general, these crossed-field switch devices comprise an inner anode surrounded by an outer cathode to define a continuous interelectrode space so that under the proper conditions an electron can orbit around the anode. Usually the anode and cathode electrodes are concentric cylinders so that an axis is defined. The electric field is radial, directly between the electrodes. A low pressure gas in the interelectrode space supports a glow discharge when the electron path is sufficiently long. The pressure is sufficiently low so that radial electron flow does not produce cascading ionization, but when an axial magnetic field is provided to the interelectrode space, the spiraling of electrons around the anode causes sufficient collisions to cause cascading ionizations. Interruption of the magnetic field causes collapse of the plasma and off-switching.
A group of the prior patents directed to the crossed-field switch device, and a number of its features include: Hofmann U.S. Pat. No. 3,558,960; Hofmann U.S. Pat. No. 3,604,977; Lutz et al U.S. Pat. No. 3,638,061; Lund et al U.S. Pat. No. 3,641,384; Lutz et al U.S. Pat. 3,678,289; Hofmann U.S. Pat. No. 3,714,510; Gallagher U.S. Pat. No. 3,749,978; Hofmann U.S. Pat. No. 3,769,537; Hofmann U.S. Pat. No. 3,873,871; Lutz et al U.S. Pat. No. 3,876,905; Lutz et al U.S. Pat. No. 3,890,520; Gallagher et al U.S. Pat. No. 3,906,270; Hofmann U.S. Pat. No. 3,947,342; and Gallagher et al U.S. Pat. No. 3,963,960. The disclosures of these patents are incorporated in their entirety into this specification.
A study of these patents shows that Lutz et al U.S. Pat. No. 3,678,289, Gallagher U.S. Pat. No. 3,749,978 and Hofmann U.S. Pat. No. 3,873,871 teach an off-switching magnetic field coil which at least pulses the main magnetic field below the critical value so that in the entire interelectrode space the magnetic field is below the critical value so that plasma collapse and off-switching occurs.
Gallagher et al, U.S. Pat. Nos. 3,963,960 and 3,906,270 discuss the arrangement of the magnetic field in the interelectrode space for conduction.
Thus, it has previously been taught that it is necessary that the magnetic field in the entire interelectrode space be pulsed below the critical value for the collapse of the plasma. Since the main field is quite strong, it requires a substantial magnetic pulse to bring the net field below the critical value and the result is considerable inductance in the field to cause difficulty in quickly reducing the main field.